In recent years, with the widespread use of electrical devices such as a motor, the likelihood that a faulty operation of an electrical device leads to a major accident has become increasingly large and thus minimization of the risk of accidents has been demanded. International Standards are defined in order to keep the risk within an allowable range. IEC61508 is defined as a standard related to electrical devices and IEC61800-5-2 is defined as a standard for drive devices such as a motor.
IEC61800-5-2 specifies a Safe Torque Off function (STO) as a safety function. In the Safe Torque Off function, the motor power is interrupted when an interruption command is received from outside. Not only for motors but for any devices, it is an important function for safety that the power can be definitely interrupted when required. To realize this function, it is necessary to periodically diagnose whether there is no fault such as disconnection or short-circuit in a circuit that transmits an interruption signal.